Microwave tube apparatus having a solid block body with drift tube cooling means



Dec. 12, 1967 L. T. ZITELLI 'ET AL 3,

MICROWAVE TUBE APPARATUS HAVING A SOLID BLOCK BODY WITH DRIFT TUBE COOLING MEANS Original Filed Oct. 50, 1961 2 Sheets-Sheet 1 INVENTORS LOUIS I ZITELLI myms MALTZER MW m 9 J 3 V Om i mm ww X\\ 3 3 v ow mm v .5 w m v Ii 3 w Q v 5 h I A n 1 m? ow mm mm WM 2 mm ww T 5 5 i mm m s; mac 8 1 mm mm m I. 3 mm m om mm s w an m N 1 mm -o Nb n9 mw mm mm QB v Q ,VNN O- E. N 2. om 9. ow L O m i I .2. mp 7 mm f o 8 mm mm s 8 r 6E ATTORNEY Dec. 12, 1967 T. ZITELLI ETAL 3,358,181

MICROWAVE TUBE APPARATUS HAVING A SOLID BLOCK BODY WITH DRIFT TUBE COOLING MEANS Original Filed Oct. 30, 1961 2 Sheets-Sheet 2 7 9 3' 3" ////////AI l "7 Q 33' I G INVENTORS LOUIS T ZITELLI IRVING MALTZER ATTORNEY United States Patent MICROWAVE TUBE APPARATUS HAVING A SOLID BLOCK BODY WITH DRIFT TUBE COOL- ING MEANS Louis T. Zitelli, Palo Alto, and Irving Maltzer, San Carlos, Califl, assignors to Varian Associates, Palo Alto, Calif a corporation of California Original application Oct. 30, 1961, Ser. No. 148,520, now Patent No. 3,281,616, dated Oct. 25, 1966. Divided and this application July 5, 1966, Ser. No. 574,856

2 Claims. (Cl. 3155.39)

ABSTRACT OF THE DISCLOSURE A high power microwave tube is disclosed. The tube includes an electron gun at one end for forming and projecting a beam of electrons over an elongated beam path to a collector structure at the other end of the tube. The collector structure collects the beam and dissipates the energy thereof. A solid block body made of a good thermally and electrically conductive material is disposed intermediate the beam forming means and the beam collector means. The solid block body includes a plurality of cavities formed therein in axially spaced relation to define a plurality of cavity resonators for interaction with the electron beam. The body includes an axially directed bore intersecting with the successive cavity resonatorn. A plurality of drift tube segments are inserted within the longitudinal bore in axial alignment therewith. The drift tube segments each include an annular recess circumferentially extending about the outer circumference of the drift tube members to define with the inner wall of the longitudinal bore a plurality of annular coolant chambers extending around the drift tube segments within the solid block body. A plurality of transversely directed bores intersect with the longitudinal bore to provide coolant passageways communicating with the annular drift tube coolant chambers. A pair of coolant distribution manifolds are formed in opposite sides of the block in communication with the transversely directed bores for providing a flow of fluid coolant through the block body and around the drift tubes for cooling same in use.

This invention is a divisional application divided out of parent application Ser. No. 148,520 filed Oct. 30, 1961, now issued as US. Patent 3,281,616 issued Oct. 25, 1966, and assigned to the same assignee as the present invention, and relates in general to CW klystron amplifiers and, in particular, to a novel high power, high frequency klystron amplifier adapted, for example, for use in space communications, radio astronomy, CW illuminators and forward scatter.

During the past few years there has been an increasing demand for higher CW power, for example, in the order of 50 kilowatts or more at X-band frequencies (7.125 to 8.5 kmc.). The graphic reuslt of a recent survey by L. S. Nergaard, RCA Review, December 1960, on power limitations of microwave transmitting tubes is depicted in FIG. 4 of the drawings. This graph shows a plot E of expected power output as a function of frequency. The article by Nergaard states that increases in power output have not been large and that a major breakthrough may be required to achieve order of magnitude improvements.

3,358,181 Patented Dec. 12, 1967 The klystron amplifier of the present invention has generated about one order of magnitude more average power than any known microwave device at X-band frequencies. Its performance data is superimposed, by an X, on the Nergaard graph of FIG. 4 and shows that an order of magnitude improvement has been obtained over the prior art. This would indicate that a major breakthrough in the state of the art has been achieved.

Some of the problems associated with increasing the power output of X-band klystrons are as follows:

One problem associated with an increase in power is that approximately 1 kilowatt of R.F. power may be dissipated within the output resonator cavity due to the high circulating currents present. This is turn may cause excessive heating of the drift tube headers, drift tube, and tuning structure of this cavity thereby impairing operation of the device from excessive thermal expansion or damage to the aforementioned structure from overheating.

Also, an increase in multipactor between opposing drift tube end portions in the last two cavities may be anticipated due to the increased beam current density present in the last two cavities.

It is the object of the present invention to provide a novel high power CW klystron amplifier tube of high frequency which is adapted for use in high power CW systems.

Another feature of the present invention is a novel cooling ssytem for removing excessive heat from the drift tubes and drift tube headers to aid in reducing thermionic expansion within these elements and to aid in reducing multipactor between opposing drift tube portions.

Other features and advantages of this invention will become apparent from a perusal of the following specification taken in connection with the accompanying drawings wherein,

FIG. 1 is a longitudinal partial cross sectional view of the novel klystron of the present invention,

FIG. 2 is an enlarged fragmentary longitudinal cross sectional view of a portion of the structure of FIG. 1 delineated by line 22,

'FIG. 3 is a fragmentary transverse cross sectional view of FIG. taken at the line 33 in the direction of the arrows,

' FIG. 4 is a graph of average power Output of state of the art transmitter tube as a function of frequency,

FIGS. 5a and 5b are fragmentary enlarged cross sectional views of FIG. 3 taken at lines 9a and 9b in the direction of the arrows.

Referring now to the drawings, the novel multicavity klystron tube of this invention comprises three main portions: a beam producing section 1 followed by a central beam interaction section 2 (best seen in FIG. 2), wherein interaction between the beam and the applied radio frequency wave takes place to produce the amplification, and a collector section 3 where the electrons of the spent beam are collected.

The beam interaction section 2 of the tube (see FIG. 2) preferably has a body formed by a substantially rec tangular block 35 of a good thermal conductor, for example, oxygen free high conductivity copper. A longitudinally directed cylindrical bore 36 passes through a number of spaced, transversely directed bores extending from a side 38 of block 35 to form a plurality of transverse headers 39 between adjacent transverse bores. Headers 39 are adapted to receive a plurality of drift tube members 40, as of copper, which are secured, as by brazing, into position within cylindrical bore 36.

Each drift tube member 40 comprises a cylinder as of, copper for example, provided with a central bore extending therethrough and through such extensions to provide a drift space 41 for the electron beam generated in the emitter section. All of the drift tube ends are beveled to aid in eliminating multipactor between opposing drift tube ends. When the drift tube members 40 are inserted in the cylindrical bores 36 in properly spaced relation, as determined by the spacing of the headers 39, resenator cavities 42 of the desired frequency are formed by the interior walled off portion of headers 39, the walled off portion being defined by the cavity portion inwardly of the movable diaphragms. A beam field interaction gap 43 is defined by the space in between the free ends of mutually opposing reentrant drift tubes 40. As best seen in FIG. 2 the first and last resonator cavities 42 are completed by drift tube members which, in effect, constitute one-half of the complete drift tube members 40 previously described.

The end portions of the drift tube members 40 extending into the third and fourth resonator cavities 42 are s'errated at 44 to further aid in reducing multipactor between mutually opposing drift tube free end portions and are also provided with double bevel angled ends. The free ends of these drift tubes are first beveled at a small angle at X to reduce the mutually opposed surface area in the interaction region between which multipactor could otherwise occur and to provide better R.F. interaction with the beam passing through drift tube 40 by concentrating the RF. fields within the beam. A second portion of the drift tubes is beveled at a greater angle, a short distance from the end of the drift tube. The enlarged beveled angle Y provides more metal at the fixed ends of the drift tubes to aid in removing excessive heat therefrom.

There are alternative ways of reducing multipactor between drift tube ends yet supplying a large mass of metal to aid in removing heat. One alternative is to provide a concave surface thereby approximating the double bevel shape in place of the double beveled surface. Another alternative would be to provide a fillet of metal between the angle formed by the two beveled segments.

Excessive heat is removed from within the rectangular block 35, headers 39 and drift tubes 40 through the following novel coolant means (see FIG. 1). Input and output fluid fittings are inserted into block 35 in a direction mutually perpendicular to a plane containing the waveguides 45 and tuning structure 4. Three transverse holes (see FIG. 3) or passages 33, 33' and 34 are bored through the transverse headers 39 to provide cooling passages for the headers and drift tubes 40. The centrally disposed passage 34 bisects the longitudinal central bore 36. Each drift tube member 40 has a drift tube coolant channel 34' cut, as by machining, around a portion of its outer periphery midway between its two ends so that when the drift tubes 40 are properly positioned within the central bore 36 and annular coolant channel 34 is formed.

FIGS. 5a and 5b show the flow diagram for the coolant passing through the passages of the drift tubes and headcrs defining a coolant flow network. Let us assume the fluid, for example water, enters from the fluid fitting closest to the output resonator cavity. Referring now to FIG. 5a, fluid enters the tube block at A, passes in the direction of the arrows, and then down through the passages 33, 33 and 34 of the last header 39 to the far side of the tube, that is the side shown in FIG. 5b. Fluid passes along channel 37 in the direction of the arrows, and back up to the next to the last header through passages 33, 33 and 34 to the near side, that is the side shown in FIG. 5a. Fluid then passes along channel 37 in the direction of the arrows and flows to the far side of the tube through the second and third headers, where it is collected and passes along channel 37 to the first header, back up the first header to the near side, that is the side at FIG. 5a, and out at 8.

To provide coupling of radio frequency energy into and out of the amplifier, (see FIG. 2) the described rectangular block 35 is cut away in its side portion for the reception of conventional waveguide section 45 which communicate with the first and last resonator cavities 42 through bored iris openings 46. Suitable R.F. windows 47 (see FIG. 1) of a wave permeable material, such as alumina ceramic are positioned at the end of waveguide sections 45 within suitable flange assemblies 48. A suitable pinch-off tube 49 is placed in gas communication with the waveguide to provide a means for evacuating the tube.

An electromagnet (not shown) operates on a power requirement of approximately 1520 watts to produce a magnetic field strength of approximately 3500 gauss. The magnet is fitted on the ends of the pole pieces 34 and 50 to provide an axially directed beam focusing magnetic field.

In operation, a beam of electrons emitted from the cathode button 11 is accelerated through the bore 13 and into the small axially aligned cylindrical drift spaces 41 and the drift tubes 40, The radio frequency signal, to be amplified, is fed into the first or buncher cavity resonator through the input waveguide 45. The radio frequency electric field produced across the resonator gap in this first cavity resonator velocity modulates the electrons, that is, the electrons are slowed down and speeded up, depending on the phase of the radio frequency field across the interaction gap 43 at the time of gap transit of the electron. In the field free drift space defined by the first drift tube member 40, the velocity modulation forms the beam into groups or bunches of electrons, which at their point of sharpest bunching, pass through the resonator gap in the second cavity resonator.

It is noted that in the present tube /2 watt radio frequency drive power is suflicient to drive the tube to slightly less than 24 kilowatts at an efliciency of 38%. The tubeis designed to operate over a limited tuning range of plus or minus 30 me. about a frequency in the X-band (7.125 to 8.5 kilomegacycles).

Several of the manufactured tubes have been tested with 21 CW. RF. power output of 41 and 43 kw. This is an improvement over state of the art X-band C.W. tubes in the order of one magnitude.

Since many modifications and variations in the described arrangement can be obviously made without departing from the scope of the invention, it is intended that all matter in the foregoing description or shown in the accompanying drawing should be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a microwave tube apparatus, means for forming and projecting a beam of electrons over an elongated beam path, means at the terminal end of the beam path for collecting the beam and dissipating the energy thereof, means forming an interaction circuit disposed along said beam path intermediate said beam forming and beam collecting means for interaction with the beam to pcoduce an output microwave signal, said interaction circuit including, a solid block of electrically and thermally conductive material having a plurality of cavities formed therein in axially spaced relation to define a succession of cavity resonators separated by axially spaced portions of said block, a longitudinally directed bore passing axially of said block through said axially spaced portions of said block and intersecting with successive ones of said cavities, a plurality of tubular metallic segments disposed within said bore and axially aligned therewith in axially spaced relation to define a plurality of drift tube members projecting re-entrantly into adjacent cavities from said axially spaced portions of said block structure, the improvement wherein, a plurality of said drift tube segments each include a circumferentially directed channel at their outer circumference for defining a succession of fluid coolant passages around said drift tubes within said block 5 6 structure, and a plurality of transversely directed bores References Cited passing into said block and intersecting with said longitudinal bore to define coolant passageways in fluid com- UNITED STATES PATENTS munication With said coolant passages around said drift 2,644,908 7/1953 Varian 315 5.38 tube segments for cooling said drift tube segments. 5 3,227,915 1/1966 Le i 313 20 2. The apparatus of claim 1 including, means forming coolant manifolds formed in said block on opposite ELI LIEBERMAN, 'y Examine!- sides of said block and communicating With said trans- S CHATMON, JR" Asst-slant Examiner versely directed bores to provide a coolant flow network for said cavity resonators and said drift tube segments. 10 

1. IN A MICROWAVE TUBE APPARATUS, MEANS FOR FORMING AND PROJECTING A BEAM OF ELECTRONS OVER AN ELONGATED BEAM PATH, MEANS AT THE TERMINAL END OF THE BEAM PATH FOR COLLECTING THE BEAM AND DISSIPATING THE ENERGY THEREOF, MEANS FORMING AN INTERACTION CIRCUIT DISPOSED ALONG SAID BEAM PATH INTERMEDIATE SAID BEAM FORMING AND BEAM COLLECTING MEANS FOR INTERACTION WITH THE BEAM TO PRODUCE AN OUTPUT MICROWAVE SIGNAL, SAID INTERACTION CIRCUIT INCLUDING, A SOLID BLOCK OF ELECTRICALLY AND THERMALLY CONDUCTIVE MATERIAL HAVING A PLURALITY OF CAVITIES FORMED THEREIN IN AXIALLY SPACED RELATION TO DEFINE A SUCCESSION OF CAVITY RESONATORS SEPARATED BY AXIALLY SPACED PORTIONS OF SAID BLOCK, A LONGITUDINALLY DIRECTED BORE PASSING AXIALLY OF SAID BLOCK THROUGH SAID AXIALLY SPACED PORTIONS OF SAID BLOCK AND INTERSECTING WITH SUCCESSIVE ONES OF SAID CAVITIES, A PLURALITY OF TUBULAR METALLIC SEGMENTS DISPOSED WITHIN SAID BORE AND AXIALLY ALIGNED THEREWITH IN AXIALLY SPACED RELATION TO DEFINE A PLURALITY OF DRIFT TUBE MEMBERS PROJECTING RE-ENTRANTLY INTO ADJACENT CAVITIES FROM SAID AXIALLY SPACED PORTIONS OF SAID BLOCK STRUCTURE, THE IMPROVEMENT WHEREIN, A PLURALITY OF SAID DRIFT TUBE SEGMENTS EACH INCLUDE A CIRCUMFERENTIALLY DIRECTED CHANNEL AT THEIR OUTER CIRCUMFERENCE FOR DEFINING A SUCCESSION OF FLUID COOLANT PASSAGES AROUND SAID DRIFT TUBES WITHIN SAID BLOCK STRUCTURE, AND A PLURALITY OF TRANSVERSELY DIRECTED BORES PASSING INTO SAID BLOCK AND INTERSECTING WITH SAID LONGITUNDINAL BORE TO DEFINE COOLANT PASSAGEWAYS IN FLUID COMMUNICATION WITH SAID COOLANT PASSAGES AROUND SAID DRIFT TUBE SEGMENTS FOR COOLING SAID DRIFT TUBE SEGMENTS. 